Experimental and observational data suggest that vitamin D supplementation reduces left ventricular hypertrophy and improves cardiac function. Prospective clinical data, however, are lacking. Thus, we propose an ancillary study to the Vitamin D and OmegA-3 Trial (VITAL) (U01CA138962), an outcomes trial of vitamin D supplementation in 20,000 men and women (aged 60 and 65 years, respectively). Because VITAL lacks any direct assessment of cardiac structure and function, we propose to perform cardiac imaging with echocardiography in 1,000 VITAL subjects pre-randomization and at 3 years. These data may answer several important questions that are not being addressed by the parent trial. Specifically, VITAL is focused on vascular endpoints (myocardial infarction, stroke), raising the possibility that important effects of vitamin D on the heart itself could be missed. Because there is compelling experimental evidence regarding the direct myocardial effects of vitamin D, assessment of cardiac structure and function would provide invaluable clinical and mechanistic insight, regardless of the outcome of the overall parent trial. The investigators have extensive experience in subclinical cardiovascular imaging, coordination of randomized trials (including the parent VITAL study), and clinical and experimental nutritional research. The study represents a unique and cost- effective opportunity to investigate measures of cardiac structure and function in a large, diverse primary prevention trial. PUBLIC HEALTH RELEVANCE: Experimental and epidemiologic evidence suggests that vitamin D has beneficial effects on cardiac structure and function. Prospective data from large-scale trials, however, are lacking. Using non-invasive imaging tests, the proposed study will examine whether vitamin D supplementation has beneficial cardiac effects, which has important public health implications.